In recent years, systems for tracking an object using, for example, an Industrial television camera, to realize continued monitoring or acquire detailed information have been produced on a commercial basis for protective service equipment employed in large-scale facilities such as airports and manufacturing plants, lifeline facilities such as electric power plants and water networks, and traffic information support systems such as Intelligent Transport Systems. These systems include not only ground equipment type systems, but also compact ones installed in vehicles, ships or airplanes and having a vibration-proof structure. In the systems, it has come to be important to enhance their whirling speed to make them quickly point a plurality of targets and sequentially track the targets.
In such a conventional moving object image tracking system as the above, to track a target that moves in all directions, a gimbal structure is often employed. The gimbal structure needs to have at least two axes. In such biaxial gimbals, when a target passes the zenith or a position near the same, it is necessary to instantly rotate the AZ axis thereof through 180 degrees. Actually, however, this quick rotation is hard to execute since the motor torque is limited, and hence the phenomenon, called gimbal lock, which makes it impossible to continuously track an object will occur. Therefore, the biaxial gimbal structure cannot be oriented to the zenith and its vicinity, which makes it difficult to realize omnidirectional tracking.
In light of the above, in some conventional image tracking systems, a triaxial gimbal structure is employed to enhance the degree of freedom in tracking, and is attempted to be used to continuously track a target in all directions, with its azimuth axis (Az axis) and cross elevation axis (xEL axis) controlled so as not to excessively increase the angular velocity to thereby avoid gimbal lock and make the movement of the gimbal fall within an allowable range.
Further, as a conventional technique that does not employ a gimbal structure, a mechanism has been proposed in which a spherical casing is rotated in all directions by a friction rolling mechanism.
Yet further, as a mechanism for rotating a spherical movable body utilizing friction, a conveyor apparatus capable of moving by rolling a spherical rotary hollow body with its surface formed of an elastic member has been proposed.
The above conventional techniques have a problem that downsizing is hard to realize and a control law for tracking a target is complex. For instance, in the triaxial gimbal structure, the number of driving means, such as motors, is increased, which makes it difficult to reduce the size and manufacturing cost. Also, since a camera, for example, is installed, the inertia load of the xEL axis is inevitably increased, which may cause interference between the Az axis and the xEL axis. Thus, problems peculiar to the triaxial gimbal structure may well occur. In addition, although it is possible to reduce the angular velocity of the Az axis utilizing a redundant axis, the angular velocity required for the Az axis is still greater than that of any other axis, whereby the driving torque needed for the Az axis is inevitably increased.
Furthermore, a system utilizing no conventional gimbal structure is free from a problem such as gimbal lock. In this case, however, it is difficult to automate the system. For instance, it is necessary to drive a spherical body by artificial remote control until a target enters the screen of a camera. In addition to this, since there is no element for acquiring information indicating the orientation of the camera, it is difficult to automatically track the target using information acquired from an image thereof. Also, since the camera, for example, in the spherical casing is accessed by radio, the timing of moving the camera is limited.
Moreover, it is difficult to apply the conventional mechanism for driving a spherical body to a moving object image tracking system, although this mechanism is applicable to, for example, a moving apparatus. For instance, it is difficult to reorient the camera to point in a desired direction, because the spherical body is driven so that a table moves with its attitude kept horizontal.